1. Field of the Invention
Generally, the present invention relates to an electric-power-assist transmission and its shift control method. In particular, the present invention relates to an electric-power-assist transmission wherein a gear shift as well as the operation to put a main clutch in an engaged or disengaged state are carried out electrically. In a situation with a small shift shock expected in a shift, switching to fast shift control is carried out from shift control for reducing the magnitude of a shift shock carried out at normal times. More specifically, the present invention relates to an electric-power-assist transmission and a shift control method wherein, with the main clutch in a disengaged state in a shift process, if the rotational speed of the engine exhibits a predicted change, control of a motor for driving the main clutch is carried out in a way different from control at normal times.
Furthermore, the present invention relates to a shift control method to be adopted in an electric-power-assist transmission whereby, if a shift-change operation is carried out with the vehicle in an all but halted state, the main clutch is released from an engaged state and a gear change is made before putting the clutch back in an engaged state quickly.
2. Description of the Background Art
In the conventional transmission, a gear shift is carried out by operating both a clutch pedal (or a clutch lever) and a shift-change lever. On the other hand, in an electric-power-assist transmission disclosed in Japanese Patent Laid-open No. Hei 5-39865, a gear shift is carried out electrically by a motor. In the conventional technologies described above, a shift drum is intermittently rotated in both directions by a driving motor so as to actuate a desired shift fork in a gearshift-change operation. On the other hand, it is possible to put the clutch in an engaged or disengaged state also by using a motor as well.
In such a case, when thinking of the conventional manual transmission, only by repeating the shift-change operation can the shift change be eventually completed even if the gear is not shifted smoothly. In addition, whether or not the clutch can be put in an engaged state smoothly after the shift change much depends on the operation of the clutch carried out by the driver.
As described above, in the conventional manual transmission, most of poor operability as evidenced by whether or not a shift change can be completed without repeating the shift-change operation or whether or not the clutch can be put in an engaged state smoothly much depends on how the operation is carried out by the driver. In other words, the driver's learning effects allow good operability to be obtained.
By driving both the clutch and the shift-change lever by means a motor, on the other hand, elements dependent on the operation carried out by the driver do not exist any more. Thus, in a state where a gear shift is impossible, if the clutch is not put in an engaged state smoothly or not in accordance with the driver's intention, it is quite within the bounds of possibility that the driver feels a sense of incompatibility.
While control is executed to engage the clutch smoothly and slowly in an ordinary shift so that no shift shock occurs, there are situations in which the clutch must be quickly placed in an engaged state. For example, in an ordinary shift-up operation, the driver normally turns on a shift-up switch after restoring the acceleration pedal. Then, after the shift-change operation has been completed and the clutch has been put back in an engaged state, the driver carries out an operation to open the accelerator. It is also quite possible, however, that the driver turns on the shift-up switch without restoring the accelerator pedal, or opens the accelerator before the clutch is put back in an engaged state.
Likewise, in a shift-down operation, the driver normally turns on a shift-down switch after restoring the acceleration pedal. Then, after the shift-change operation has been completed and the clutch has been put back in an engaged state, the driver operates the accelerator pedal. It is also possible, however, that in a shift-down operation, the driver revs the engine in order to adjust the rotational speed of the engine to a rotational speed after the shift down. In this way, since the operation of the acceleration pedal in a shift change may vary from driver to driver, various kinds of control adjusted to the operation are required.
When putting the clutch back in an engaged state after being released from an engaged state, for example, it is desirable to put the clutch in the engaged state slowly in order to reduce the magnitude of a shift shock generated while the vehicle is running. With the vehicle stopped, however, it is desirable to put the clutch in the engaged state quickly because no shift shock is generated anyway.